The spectacle of four generals in an Arab country's security services being hauled in for questioning over the assassination of a politician is not just unusual. It is unique. Yet that is what happened in Beirut this week, as a United Nations-mandated investigation into February's murder of Rafiq Hariri, the former Lebanese prime minister, enters its final days. Every bit as much as the "Cedar Revolution" in Lebanon this spring, this is a moment to savour.

The arrests suggest to the Arab public that the national security states and intelligence services that dominate them can be held accountable, for all the impunity with which they exercise their tyranny. That idea is profoundly subversive of the region's autocracies - and altogether welcome.